This invention relates to semiconductor detector systems in general, and more specifically, to scanned infrared detector systems.
As resolution requirements for all types of infrared detecting systems have increased, the size of the individual detector in an array has been reduced. As a result of this reduced size, detectors found in systems currently in use have only a limited charge storage capacity in relation to the dwell time required. This shortcoming in detectors is due to the fact that present detectors become saturated within the period of dwell times presently used. If not for this problem, a single sample of a detector would be sufficient, and less circuitry would be required for processing of array output signals. However, due to the state of the art in detector materials and performance, in that detectors are inadequate to store the charge which they would collect in a typical dwell time, most scanned detector infrared systems require some form of signal conditioning on the focal plane. One method for accomplishing this signal conditioning is to accumulate detector samples on a switched capacitor. This method allows a detector to be sampled and reset a number of times per dwell time. The result of this action is a weighted sum of detector samples capacitively stored. The accumulation of samples creates a gain, which varies directly with the number of samples taken. This gain acts to improve the signal to noise ratio of the array output signals.